Servicio de Microbiología and Unidad de Investigación, Instituto Universitario de Investigación en Ciencias de la Salud (IUNICS), Hospital Universitari Son Espases, Ctra. de Valldemossa 79, 07014 Palma de Mallorca, Spain.
Antimicrob Agents Chemother. 2011 Oct;55(10):4560-8. doi: 10.1128/AAC.00519-11. Epub 2011 Aug 1.
Pseudomonas aeruginosa has an extraordinary capacity to evade the activity of antibiotics through a complex interplay of intrinsic and mutation-driven resistance pathways, which are, unfortunately, often additive or synergistic, leading to multidrug (or even pandrug) resistance. However, we show that one of these mechanisms, overexpression of the MexCD-OprJ efflux pump (driven by inactivation of its negative regulator NfxB), causes major changes in the cell envelope physiology, impairing the backbone of P. aeruginosa intrinsic resistance, including the major constitutive (MexAB-OprM) and inducible (MexXY-OprM) efflux pumps and the inducible AmpC β-lactamase. Moreover, it also impaired the most relevant mutation-driven β-lactam resistance mechanism (constitutive AmpC overexpression), through a dramatic decrease in periplasmic β-lactamase activity, apparently produced by an abnormal permeation of AmpC out of the cell. While these results could delineate future strategies for combating antibiotic resistance in cases of acute nosocomial infections, a major drawback for the potential exploitation of the described antagonistic interaction between resistance mechanisms came from the differential bacterial physiology characteristics of biofilm growth, a hallmark of chronic infections. Although the failure to concentrate AmpC activity in the periplasm dramatically limits the protection of the targets (penicillin-binding proteins [PBPs]) of β-lactams at the individual cell level, the expected outcome for cells growing as biofilm communities, which are surrounded by a thick extracellular matrix, was less obvious. Indeed, our results showed that AmpC produced by nfxB mutants is protective in biofilm growth, suggesting that the permeation of AmpC into the matrix protects biofilm communities against β-lactams.
铜绿假单胞菌通过内在和突变驱动的耐药途径的复杂相互作用，具有逃避抗生素活性的非凡能力，不幸的是，这些途径往往是相加或协同的，导致多药（甚至泛耐药）耐药。然而，我们表明，这些机制之一，MexCD-OprJ 外排泵的过度表达（由其负调节因子 NfxB 的失活驱动），导致细胞包膜生理学发生重大变化，损害了铜绿假单胞菌固有耐药性的骨干，包括主要组成型（MexAB-OprM）和诱导型（MexXY-OprM）外排泵和诱导型 AmpC β-内酰胺酶。此外，它还通过剧烈降低周质内β-内酰胺酶活性，削弱了最相关的突变驱动β-内酰胺耐药机制（组成型 AmpC 过表达），显然是由于 AmpC 异常渗透出细胞所致。虽然这些结果可以为急性医院获得性感染情况下的抗生素耐药性的未来策略制定提供依据，但由于生物膜生长的细菌生理学特征存在差异，这是慢性感染的标志，因此描述的耐药机制之间的拮抗相互作用的潜在利用存在一个主要障碍。虽然 AmpC 活性无法在周质中浓缩，这极大地限制了β-内酰胺类药物在单个细胞水平上对靶标（青霉素结合蛋白 [PBPs]）的保护，但对于作为生物膜群落生长的细胞，其预期结果并不明显，这些细胞被厚厚的细胞外基质包围。事实上，我们的结果表明，nfxB 突变体产生的 AmpC 对生物膜生长具有保护作用，表明 AmpC 渗透到基质中可保护生物膜群落免受β-内酰胺类药物的侵害。
